Re: Planning counters in pg_stat_statements (using pgss_store)

Hello,

On Sun, Sep 8, 2019 at 11:45 AM Imai Yoshikazu <yoshikazu_i443@live.jp> wrote:
>
> I also saw the codes and have one comment.

Thanks for looking at this patch!

> [0002 patch]
> In pgss_planner_hook:
>
> +               /* calc differences of buffer counters. */
> +               bufusage = compute_buffer_counters(bufusage_start, pgBufferUsage);
> +
> +               /*
> +                * we only store planning duration, query text has been initialized
> +                * during previous pgss_post_parse_analyze as it not available inside
> +                * pgss_planner_hook.
> +                */
> +               pgss_store(query_text,
>
> Do we need to calculate bufusage in here?
> We only store planning duration in the following pgss_store.

Good point!  Postgres can definitely access some buffers while
planning a query (the most obvious example would be
get_actual_variable_range()), but as far as I can tell those were
previously not accounted for with pg_stat_statements as
queryDesc->totaltime->bufusage is only accumulating buffer usage in
the  executor, and indeed current patch also ignore such computed
counters.

I think it would be better to keep this bufusage calculation during
planning and fix pgss_store() to process them, but this would add
slightly more overhead.


> We only store planning duration in the following pgss_store.
>
> --
> Yoshikazu Imai